Application of fans is increasing along with the rapid development of industrial techniques. For example, fans in heat exchangers or computer equipment can make a temperature therewithin drop. Specifically, an axial flow fan directly blows air over the computer equipment or rapidly circulates the air to cool the equipment.
FIG. 1 shows a three-dimensional view of the blades of the axial flow fan the prior art. The axial flow fan has a hub 100 and a plurality of blades 102. Each of the blades 102 equally extends from periphery 104 of the hub 100. Air drifts into the region of the blades 102 and then the air around the blades 102 is compressed to form airflow when the axial flow fan spins in a direction 106.
FIG. 2 shows a cross-sectional view of a blade 102 of the axial flow fan depicted in FIG. 1. An incident angle 112 is defined as an angle between a line 108 and the flow direction 110 of the air. The line 108 is drawn between a leading edge and a rear edge. There is a separation between the air and the surface of the blades 102 resulting in a stall effect when the incident angle 112 increases up to a specific angle. Turbulence is then formed on the upper surface of the blades 102. Since the stall effect reduces the work generated by the blades, the efficiency of the axial flow fan is severely decreased.